Radiation can be transmitted through optical waveguides, such as thin transparent fibers referred to as optical fibers. The semiconductor light emitting diode emits a stable source of radiation, referred to herein as light. Coupled light emitting diodes are used for introducing optical signals into an optical fiber and coupled photodiodes are used for detection of light signals to provide electrical signals at the receiving end.
In the emission mode of the diode, coupling refers to the reception in the optical fibers of light produced by the recombination of holes and electrons in the diode. In the detection mode, coupling refers to the absorption of photons received from the optical fiber which results in the production of electrical charge carriers. In gallium aluminum arsenide diodes, for example, a forward bias on the diode causes the injection of electrons from the n-type regions into the p-type regions; the electrons injected into the active p-type region of the diode recombine with holes present therein, giving up energy in the process to form photons of light.
In the detection mode the process in reverse produces electrons and holes from the photons.
The quantum efficiency of this conversion in the emission mode is determined by the ratio of photons in a given waveguide to the number of carriers converted to photons in the diode.
In the detection mode the quantum efficiency of the diode is defined as the ratio of the number of charge carriers produced at the electrical output to the number of photons entering the diode.
The system of U.S. Pat. No. 3,952,265 issued Apr. 20, 1976 to R. G. Hunsperger et al. provides a unitary dual mode diode which can function as an emitter or detector. Basically this dual mode diode is a p-n junction that functions as a laser when forward biased, a photodiode when reverse biased, and with no voltage applied when in the neutral state has a relatively low insertion loss which does not interfere with the functioning of other devices on the transmission line.
In the unitary emitter-receiver semiconductor diode device of U.S. Pat. No. 4,773,074 issued Sep. 20, 1988 the p-n junction is formed between a heavily doped active layer of one conductivity type and a lightly doped wave guiding layer of opposite conductivity type so as to improve the efficiency of both the emitter and receiver modes.
A dual mode emitting diode/detector diode for optical fiber transmission lines of copending U.S. application Ser. No. 07/247,042 filed Sep. 20, 1988 by Garfield Simms and R. G. Hunsperger provides direct coupling of an optical fiber to the diode at a lateral surface which is parallel to the p-n junction so that in the forward biased emitter mode the optical power from this lateral or parallel surface is substantially greater than the side-edge emission of the diode.
It is an object of this invention to provide a unitary emitter-detector semiconductor diode device with improved coupling efficiency.
Another object of this invention is an improvement in a unitary emitter-detector semiconductor diode device which reduces losses from a Lambertian emission pattern.
It is still another object of this invention to provide a unitary emitter-detector diode which can transmit in both directions from surfaces parallel to the p-n junction.
A further object is providing surface-oriented coupling to a unitary emitter-detector diode which has improved effectiveness with optical fibers or other waveguides.
A still further object is to provide a unitary emitter-detector semiconducting diode which in the quiescent or off mode will pass a signal through the diode between opposed fibers with low loss of signal.
These and other objects will be apparent from consideration of the following description with the accompanying drawings and claims.